Aircraft automatic pilot



'E. R. TRIBKEN ET AL AIRCRAFT AUTOMATIC PILOT Jan. 27, 1959 Filed Oct. 20, 1955 wir; wl

2,870,919 AIRCRAFT AoroMArlc PILor Y Everett R. Tribken, Garden City, and Stanford A. Fingerhood, New York, AN. Y., assignors to Sperry Rand 'Cor-1 poration, Great Neck, N. Y., a corporation of Dela- Ware Application October 2'0, 1955, Serial No. 541,864`

16 claims. (ci. 244-79) l pilots wherein displacement type gyros are employed such as, for example, a directional gyro for providing a directional reference for the automatic pilot and a vertical gyro for providing pitch and roll reference for Athe automatic pilot. Both` of these gyros are essentially long period devices deriving their long period control from earth base references such as the earths magnetic eld and gravity respectively. In such automatic pilots short period stabilization lis derived by obtaining higher `derivatives of the displacement signals produced by the long term references, i. e., thefdirectional and vertical gyros. Another general automatic pilot category are those in which aircraft reference gyros, rate gyros, or director gyros are employed for short period stabilization. Autopilots employing the `latter type devices or gyros may be termed rate-maneuvering systems, the maneuver com mands thereto being in terms of rates of craft movement about the craft axes. In aircraft automatic pilots ofthe latter type, long period or displacement stabilization is derived through earthbase references such as, for example, pendulums for pitch and roll references `andthe earths magnetic eld `for yaw or directional reference.

The automatic pilot of the present invention includes the advantages derived from displacement-type gyros and also some ofthe advantages of the aircraft reference gyros, at least insofar as the directional reference is concerned. ln automatic pilots using displacement type gyros which are slaved to earth basedreferences, the main objection is that the craft maneuvers are restricted by the gimbal configurationof the gyro elements. Thus, automatic pilots of this `type are generally `applicable only to large aircraft of limited maneuverability, such as, bomber aircraft and commercial transport aircraft. automatic pilot constructed in accordance with the teaching of the present invention is `admirably adapted to fighter and interceptor type aircraft which arerelatively highly maneuverable. AThe `automatic pilot of the present invention will permit high maneuverability under complete automatic control through a novel gimbal configuration of the directional gyro; maneuvers of 360 in roll and up to i80 maneuvers in pitch. This increase in craft maneuverability is obtained by supporting the gyro gimbal in the craft for freedom about an axis parallel to the craft fore and aft axis, and supporting the rotor case in the gimbal for freedom about a vertical axis normally parallel to the crafts 'vertical axis whereby 'the gyro spin -axis is horizontal, and by providing means for maintaining thefspin axis of the 4g'yro at right angles However, an

n 2,870,979 Patented Jan. 27, 1959 ICC to the plane of the .gimbaL i. e., at an angle of substantially from the fore and` aft `axis -of the airplane.

The latter is accomplished by 'the properslaving of the gyrospin axis to a long term heading-reference such as provided by a stabilized earths magnetic field detection device. It will be understood, however, that any long term heading reference may be employed, such as, for example a three gyro "stabilized platform and the like. Furthermore, with this gimbal configuration the inner gimbal angle, under` "zero `pitch lattitude conditions provides a measure ,of` craft yaw angle which is not affected by craft roll attitude and by slaying the gimbal to a vertical gyro the inner gimbal angle, under most pitch maneuvers provides a measure of craft yawangle error with respect to the earths verticali e. `the inner gimb'al angle is .tl/ cos `6l, where be is the yaw angle errorof the craft in the earth coordinates system and 0 is the craft pitch angle. fore correct for use in the craft rudder-elevator servos after `resolution for roll angles only. `It will be noted that with this 'gyro configuration, gimbal lock is avoided since the craft is controlledthrough the gyro to maintain its fore and aft axis always at right angles to the gyro spin axis. p

rThe principal` object of the present invention therefore is to provide `gyroscopic controlapparatus for aircraft wherein unlimited `roll maneuver may be made under continuous control by `said gyro apparatus.

Another object of the presentinvention resides inthe provision of gyroscopic `control `apparatus for aircraft wherein the directional reference for the craft includes a free gyroscope having the spin axis thereof oriented `at right angles to thelfore" and aft Acraft axis.`

A further object ofthe presentinvention resides in the provision `of aheading reference for aircraft automatic pilots wherein the lgim'balling of a directional gyro is such that `the yawrmeasureprovided thereby is unaffected by roll maneuvers of the aircraft.

Another object of the vpresent invention resides inthe provision of` an autopilot `system wherein the short term directional reference comprises agfree gyroscope for providing a measure of the yaw attitude of the craft `which is unaffected by rollmaneuvers and by most pitch 'maneuvers, the gimbal configuration of the gyroscope being such that the innerfginibal angle' `measures yaw deviations while the outer `gimlial langle islmaintained vertical by means of 'a verticallgyroscope. p

A further object ofthe present invention is to provide a heading Vreferenceffor aircraft which comprises a directional gyro'scope havinga rotor bearing case for supporting `the rotor sothat `it` is spun about a horizontal axis and wherein `the `gimbahsuppor'ts the rotor case for anguiar movement abouta normally vertical axis, the gimbal itself being pivotally supported in the `aircraftfor angular `movement about the crafts longitudinal axis or roll axis, and wherein mearisresponsive to -alheaiding reference device is provided `for `maintaining the crafts` longitudinal-axis `substaritially at right iangles tot the spin 'aX'is of the'gyro and also `wherein the gimbal ring is slaved to the vertical, i. `e.,rthe gyto spin-axis is maintained hori- 4z'ontalthrough averltical reference `device such as a Igyro vertical.

Other objects of the present -inventioninotfatrthis time more particularly enumerated will become apparent from the followi'ngidetailed Idescription fof fa preferred embodi- Referring now `tothe drawing, it `will be observed `that l the automatic pilot of lthe "present invention-comprises generally a command` control system represented by the reference character 1, a f stabilization V.system comprising a verticaly 4gym M18 "and a `directicmal 'gyro f5 for .-2 stabilizing A signal proportionalto this measure is theref is such that gimbal errors due to craft roll attitude.

are eliminated. The directional gyro 5 comprises a rotor (not shown) mounted in a rotor bearing case or inner gimbal member for spinning about a first horizontal axis y normally parallel tothe athwartship or pitch axis of the aircraft, i. e. when aircraft flies 'with wings level. Rotor case 10 in turnis provided with suitable trunnions for supporting the samein a gimbal ring 12 for pivotal movement therein about a vertical axis normally parallel to the craft vertical axis, i; e. when craft flies level. Gimbal ring 12 is pivotally supported on trunnions journalled in suitable bearings in the aircraft, schematically represented by reference character 13, for pivotal movement about a second axis x parallel tothe crafts fore and aft axis. Directional gyro 5 is further provided with atorque motor'14 having one part thereof fixed on the craft and the other part fixed on the outer gimbal ring trunnion for precessing the gyro about its z axis. A second torque motor 16 having one part thereof fixed on gimbal 12 and the other part thereof fixed on the rotor case trunnionis provided for precessing the gyro about its x axis. Suitable signal generators are also provided for supplyingsignals corresponding to the relative orientation of the gyro gimbals with respect to the craft. The signal generators used in the system are preferably of the selsyn type and may be referred to hereinafter as synchros. Signal generator 26, having one element fixed on the gimbal 12 and the other fixed on the rotor case trunnion, is provided for producing an output signal corresponding to the orienta tion of the rotor case 10 relative to the gimbal 12 about the gyro z axis and likewise a similar signal generator 36 having an element thereof fixed on the craft and the other element thereof fixed to the gimbal trunnion is provided for producing a signal output corresponding to the orientation of the gimbal 12 about the aircraft longitudinal axis. A conventional power amplifier is provided between synchro 26 and torquer 14 for providing required power for the torquer. A similar amplifier is provided between synchro 36 and torquer 16.

Vertical gyro 18 is a conventional non-tumbling gyro and comprises a rotor supported in a rotor case for spinning about a normally vertical axis in a suitable horizontal gimbal ring which in turn is supported in the aircraft thereby to provide a universal support for the rotor case. The rotor case is slaved to gravitational vertical in a conventional manner as by means of suitable gravitationally responsive devices such as liquid levels 55 and 56 which actuate torque motors S7 and 58 on the` roll-and pitch axes, respectively of the gyro 18` through suitable torque motor amplifiers 59, 60 respectively. Vertical gyro 18 is provided with signal generators or pick-offs which are preferably of the selsyn type, pitchpick-off 42 providing a signal output corresponding to the pitch attitude of the craft and roll pick-off 17 for providing a signal corresponding to the roll attitude of the aircraft.

In accordance with the present invention, gimbal ring v12 of directional gyro S'is maintained in a vertical plane fore detected at 36. This dierence is representedby an output signal from synchro 36 and is suitably-amplified in the torque motor amplifier and applied to roll torquer 16 whereby to pre'cess gimbal ring 12 until the difference signal from synchro 36 is zeroed. In this matter, the spin axis of directional gyro 5 is maintained horizontal and the headingy error signal output therefrom is unaffected by roll attitude and most pitch attitudes say, plus or minus pitch angles.

Not Vonlyris the spin axis-of the directional gyro 5 continuously horizontal, but in accordance with another object of the present invention it is at all times substantially at right angles to the orientation of the Icrafts longitudinal axis. If the gyro should tend to drift,a slow or long period phenomena, it will be slaved back to its former position by the magnetic reference. However, if the craft deviates from a desired magnetic heading, a fast or short period phenomenon, it will be returned to its original heading as "determined by the gyro orientation, through the craft servo systems. In either event the relationship between the gyro spin axis and the craft fore and aft axis is continuously maintained. For this purpose, a magnetic reference device, such as a preferably stabilized fiux valve 15, is provided for determining the orientation of the longitudinal axis of said craft with respect to the earths magnetic field, i. e., with respect to the horizontal component of the magnetic north vector. Such a magnetic reference device is disclosed in more detail in U. S. Patent No. 2,539,411 which is assigned to the same assignee as the present inventiori'anduwhich may be stabilized, by means of 'a conventional data repeater system, to the vertical gyro 18. Synchro or control transformer 26 includes a polyphase or three-phase stator winding fixed to gimbal 12 and hence fixed with `respect to i the heading of the aircraft, the three-phase windings thereof being respectively connected with the three-phase windings of flux valve 1S through a polyphase differential synchro 25. The function of the latter synchro will be hereinafter more fully described. The resultant magnetic field produced by the three-phase winding of synchro transformer 26 depends upon the heading of the craft with respect to direction of the earths magnetic field and the position or orientation of synchro 2S. However, in accordance with the present invention, the polyphase winding or stator of signal transformer 26 is mounted on gyro `gimbal 12 in such a manner that the windings thereof are exactly 90 displaced with respect to windings of ux valve 15. The single phase winding of synchro 26 is positioned in accordance with 'the orientation of the gyro rotor case 10, i. e., in accordance with the orientation of the gyro spin axis y. Since thepolyphase winding of synchro 26 is fixed (90 displaced) relative to the angular position of the pickup coils of fiux valve i5 in the earths field, the signal generated in the single phase winding of synchro 26 is proportional to the changes in the heading of the craft. That is upon angular displacelment of the flux valve legs relative to the earths field and A. C. signal will be generated in one or the opposite phase in the single phase winding of synchro 26 depending upon the direction of such displacement. This signal is supplied to heading torquer amplifier nad heading torquer 14 to cause precession of the directional gyro spin axis y to bring it into relative agreement with the directional reference provided by the flux valve 15. Since the three-phase winding of synchro 26 is 90 displaced from the reference direction defined by flux valve 15, the zero position of the single phase winding vof the synchro is also 90 displaced from this reference direc-tion and therefore the orientation of gyro spin axis y which produces zero signal output from synchro 26 will also be substantially 90 displaced from the reference direction defined by flux valve 15. In this manner the gyro spin axis may be said to be slaved to the magnetic reference and long period drift of the gyro spin axis is eliminated.

A signal generator 19 which ymay be of ,the selsyn conventional manner.

assuma `one of which is mounted to rotate with the craft in aziiii'lith` and the other of which is` positioned by the rotor case 10. The output of the signal generator 19 is supplied to cross control resolver-multiplier 27 to control rudder servo system 2 and elevator servo system 4 in accordance with the magnitude of the bank angle of the aircrft. This roll resolution is provided for correcting for the cross-control action between yaw and pitch maneuvers of the aircraft at 90 bank angles, as` more fully described in U. S. Patent No. 2,571,106, which patent is also assigned to the same assignee as the present invention. As waspointed out above, the gyro configuration of the present invention eliminates the requirement for pitch resolution since the output signal of synchro 26 is a measure of the gyro inner gimbal angle which angle is equal fo craft heading error, with respect to earth axes, times the cosine of "the pitch angle. This is the required signal for direct control of the rudder and no pitch resolver is needed as would be the case if the rudder signal were taken `from an azimuth pick-off of a directional reference which is stabilized in pitch. Thus if the craft should deviate from its desired heading due to short term `disturbances such as wind gusts or the like, the rudder will be deflected to cause the craft to be returned to its `desired set heading. The stator windings of gyro output signal generator or synchro 19 are so positioned on gimbal 12 that the output signal in its rotor windings is zero when the spin `axis y of" gyro 5 lies at an angle of 90 with respect tothe crafts longitudinal axis.

, The maneuver command control indicated by reference character 1 includes means for selecting a desired course or headingto be flown and also for selecting a desired pitch attitude to `be maintained or stabilized by the automatic pilot of the present invention. The turn command system illustrated in the drawing is of the heading type, that is, one` in whichthe pilot rotates command knob 20 toca desired aircraft heading and the aircraft turns "until the new desired heading is achieved. Mounted on up synchro 21'. The three `phase stator of synchro 21 Y is fixed relative to the craft, the single phase rotor of 'which is positioned by a heading follow-up motor 24 which drives heading follow-up shaft 22. Any difference between the position of motor shaft 22 and the setting of heading command knob 20 results in a signal being generated at the single phase stator of heading command synchro 21 which `is applied to heading command follow-up amplifier and limiter 23, the output `of which controls heading follow-up motor 24 and rotates the same through suitable gear train 22' until the error signal is reduced to zero. The heading error signal from heading command synchro 21 is limited before application to heading follow-up amplifier 23 so that no matter how large a heading command is selected or ordered, the maximum value that the signal may obtain cannot exceed a predetermined magnitude. In this manner, the speed with which heading follow-up motor 24 drives in response to the heading error signal is limited, this speed -being proportional to a predetermined rate of turn of the craft as will be explained.

Also driven by heading follow-up motor 24 through shaft coupling 22 is flux valve differential signal trans forming device such as differential synchro 25. This ispositioned by rotor shaft 22. One of the three phase `windings of differential synchro `25 is connected to receive the output of flux valve 15 and the other output winding thereof is connected `as an input to the heading slavng synchro 26. f i

Mounted on heading command knob 20 is a turn-bank commandsynchro 28 coupled with a bank differential synchro 30 mounted on heading follow-up motor shaft 22 for actuation by heading motor 24. The error between the `shaft positions of the heading command synchro and the heading follow-up synchro is measured by the turnbank command synchro 255` and the bank differential synchro 3i). This error is detected by means of a bank follow-up synchro 31 on the output shaft 32 of a bank follow-up motor 33. The output of bank follow-up synchro 31 is supplied through a suitable limiter to bank follow-up amplifier 29 which energizes vbank `follow-up motor `33 to position the same in accordance with the difference between the shaft positions of headingfollowup motor 24 and heading command knob 20. In 'other words, the position of bank follow-up shaft 32 is proportional to `the difference between `the present heading of the aircraft and` the desired heading thereof. Again, speed feedback is used in the bank follow-up servo loop for stabilizing the loop in accordancewith conventional servo techniques. Mounted on bank follow-up motor shaft 32 is a bank command synchro 34 having a fixed three phase stator winding connected with the respective three phase windings of roll synchro 17 on vertical gyro 18, the single phase stator `of the latter synchro being energized from a suitable source of alternating voltage. The single phase output winding of bank commandsynchro 34 is then proportional to the `difference between the actual bank angle of the craft as measured by vertical gyro 1'8 and that commanded by the magnitude of the heading error. This output signal constitutes the bank command signal `for the automatic pilot system and is accordingly applied to the aileron servo system 3 which positions the ailerons of the craft and causes the craft to bank until the actual bank angle of the craft as measured by gyro 13 corresponds to `that commanded through bank followup loops 29, 33, 32. In order that the bank angle be prevented from exceeding a predetermined value, a limiting device, such as mechanical limiter 50 is mounted on the bank follow-up shaft 32, a suitable slip clutch 51 being provided for preventing damage to the bank followup motor 33.

Furthermore, in accordance with an object of the present invention the Iactual bank angle of the craft as measured by vertical gyro 18 is compared with the position of gimbal ring 12 of directional gyro 5l as by means of synchro 36 mounted on the gimbal trunnion. The output of synchro 36 is proportional to the difference between `the bank angleof the craft and the orientation of gimbal 12, as will be produced by a combined pitching and rolling maneuver, this output being suitably amplified and applied to torquer 16 which accordingly applies a torque on the rotor case 10 to thereby precess gimbal 12 to maintain the latter vertical and hence to maintain the spin axis y of gyro 5 substantially horizontal regardless of craft bank and pitch angle coupling effects on the gimbal system.

The aircraft is conventionally stabilized in pitch by means of vertical gyro 18 and pitch synchro 42 mounted thereon, any deviations in pitch attitude of the craft `being detected thereby to provide a pitch error signal which is applied to elevator servo system 4 through resolver 43. A pitch command control is provided in the maneuver command control 1 and comprises a pitch command synchro 41 which operates to change the reference of the vertical gyro 18 in a conventional manner.

The `operation -of the automatic pilot of the present invention hereinabove described should be clearly evident from the foregoing description, but will, briefly be outlined at this time. Assume firstt'hat the aircraft is cruising straight and level at some selected heading, say, a northerly heading. Under such conditions "the output of heading yfollow-up amplifier 23 and motor 24 is zero and hence the follow-up shaft 22 isrstationary, the position of which corresponds to the heading of th-e craft. A compass card (not shown) may be attached to this shaft if desired and may cooperate with a heading selector pointer actuated by command knob 20. Also, since there is no difference between the position of head- 4ing follow-up shaft 22 and the position of heading cornmand knob 20, bank follow-up loop 29, 33, 32 is stationary and commands no bank angle. Since the selected or commanded heading is northerly, and sin-ce the resultant magnetic vector in the three phase winding of flux-valve 15 always corresponds to magnetic north, this resultant magnetic vector is repeated unchanged or unmodified atv the gyro slaving synchro 26. Should the gyro experience a long term drift, such drift would be detected at slaving synchro 26 resulting in a slaving sig- ,nal being supplied to slaving or heading torquer 14 of directional gyro to thereby precess the gyro into correspondence with the direction of the magnetic vector. However, as stated, the spin -axis y of directional gyro 5 is so slavedrto the magnetic reference or flux valve 15 rthat it is maintained 90 degrees displaced from the crafts longitudinal axis, the direction of which is deterheading selector dial (not shown), thereby producing an angular difference between the position of heading selector knob 20 and the position of heading follow-up shaft 22. Heading follow-up synchro 21 and heading command synchro 21 detect this difference and supply a signal to the input of heading command follow-up amplifier 23. Heading follow-up motor 24 responding to the output yof amplifier 23 begins to rotate at a speed proportional to the magnitude of the limited input signal thereby rotating follow-up shaft 22 in a direction to reduce the difference between the positions of shaft 22 and heading selector knob 20 to zero.

Simultaneously, with the generation of the heading command signal at synchro 21 proportional to the difference between the positions of shaft 22 and command knob 20, a bank command signal, also proportional 'to the angular difference between the positions of these two shafts, is produced through synchros 28 and 30 and applied to bank follow-up synchro 31, the output of this latter synchro being supplied after suitable limitingto bank follow-up amplifier 29, Through the bank followup servo loop, thekposition of shaft 32 is proportional to the magnitude of the difference between the positions of heading follow-up shaft 22 and command knob 20, i. e., the heading error. The rotation of bank angle command synchro 34 produces a control signal to aileron servo -channel 3 which actuates the ailerons of the craft to bank the same to an angle corresponding to the position of bank follow-up shaft 32 as measured by roll synchro 17 on vertical gyro 18. In other words, the craft will bank through an angle proportional within limits to the magnitude of heading error signal and thereby produce a rate of turn of the craft proportional, within limits, to the heading error.

As th-e craft banks, the inertial qualities of gyro 5 will maintain the gyro spin axis horizontal. However if the craft pitches while in a banked condition any precesysion of the gyro about the `craft vertical axis will pronsA axis vof gyro 5 is slaved to'vertical gyro 18 during pitch? ing' maneuvers of theaircraft` and hence the plane of the gimbal ring of vgyro 5 is maintained vertical with respect to the earth. Thus, with this` directional gyro configuration as compared with more conventional configurations gimbal lock and gimbal errors due to banking of the craft are eliminated.

At this point it should be noted that the -response characteristics of the heading follow-up servo loop and the bank follow-up servo loop is slow as compared with the natural frequency of the aircraft in yaw and roll such that the aircraft responds in rollvand yaw to the signals supplied thereby with complete faithfulness.

As the aircraft turns in azimuth in response to craft banking produced by the heading follow-up loop and bank follow-up loop, flux valve 15, being fixed to the craft in azimuth, will also turn relative to the earths field. Since the magnetic vector defined by the output windings of the fiux valve legs corresponds to a fixed direction in space, this magnetic vector, reproduced in the fixed field of differential ux valve synchro 25, will also rotate. If the turn is coordinated, the rate of rotation of the magnetic vector and the stator of differential liux valve of synchro 25 produced by flux valve 15 will rotate at the same rate that the heading follow-up shaft 22 rotates (and therefore the rotor of differential ux valve 25) and the gyro 5 willl then be precessed at'the same rate thereby producing no output to the rrudder servo system 2. However, if the turn is uucoordinated, as during turn entrance and turn exit, or if skidding or slipping occurs during the turn, a coordination signal will be developed at lateral accelerometer 35 thereby to correct the rate of rotation of heading follow-up shaft 22 and hence speed up or slow down the movement of the rotor of differential flux valve synchro 25 with respect to the rate of rotation of the magnetic vector therein, The resulting difference in the rates of rotation of the rotor of synchro 25 and the magnetic field or vector in the stator thereof will cause a change in the precession rate of gyro 5 through gyro slaving synchro 26 and torquer 14 about the gyro vertical axis. Hence a rudder command signal will be generated at pick-off 19 to deflect the rudder to correct the craft rate of turn untilthe lateral accelerometer signal is zeroed. The craft will conf tinue to turn so long as there is any difference between the positions of follow-up shaft 22 and the commanded position of heading command knob 20.

In this manner as the craft turns with zero pitch attitude about the vertical axis of the ear'ths coordinate system, the spin axis of gyro 5 will also be caused to turn about the gyro z axis and therefore the gyro spin axis will be maintained in a predetermined angular orientation with respect to the aircraft fore and aft or x axis, this predetermined orientation being substantially displace therefrom, as described above. However, if the craft turns while in a pitched attitude, the slaving of the gimbal ring of gyro 5 to the vertical gyro 18 will remove the effects `of precision of the gyro about the craft vertical axis.'

As the new heading is approached, the relative position of shaft 22 and the selector knob 20 approach correspondence, thereby reducing the heading command signal from synchro 21. As stated, during the coordinated tum, kthe magnetic vector in the stator of differential flux valve synchro 25 is in substantial synchronism lwith the rotor thereof. However, as the new heading is approached,

shaft 22 is slowed down resulting in a signal output fromI synchro 25 which will reduce lthe rate of precision of gryo 5 and a corresponding reduction in craft bank angle thereby reducing the turning rate of the craft. When there is no error between the heading command synchro 21 and headingfollow-up synchro 21', the airplane has achieved its desired heading and the bank angle commanded will also be zero. The craft will then proceed on its new heading in straight and level flight.

It will be noted that with the automatic pilot configuratherefor tor-controlling the azimuthal.; orientation apn-ogame@ tion `of the` presentinvention, gustdist'ur-bances acting on the craft` in yanl will have onlya` veryfsmallt or secondary effect on the bank attitude off the craft because-the heading follow-up loop` has a slow response to these transient yawdisturbances.

Since many changes couldhe made inthe above con strutcion and many apparently widelydiiferent embodiments; of this invention could be `made without departing from the scope thereof, it` is intended" that all matter contained in the above description -or shown in` the 10 accompanying drawings" shallbe interpreted as illustrative and ,not ina limiting sense.`

What is claimed isz l2. Aheading reference for aircraft comprising a mag-` noti-o.` device for determining the orientation of' the longi- 15 tudinal axis of said craft through interaction with the earthsmagneticeld; a directional` gyroy having a rotor, a-rotor'A caseusupporting` said rotor fo-r--spinning-about a horizontal spin axis, a ,gimbal for pivotallyfsupporting said-rotor case-for movement aboutfa second;` normally vertical aXis, means` for `supporting saidgimbal in saidaircraft for pivotal movement` aboutka third" normally horizontal axisparallel: to the longitudinal axis ofsai'd` aircraft, means` responsive to said; magnetic device for maintaining `said` spin iaxisat substantially right. angles to the-orientation of said craft longitudinal? axis as deter-- minedby said magnetic device, means-for determining thefbank angle of said craft; and means -coupljedrkwith` Said." gimbaltandA responsive totsaid last-.mentioned means for rotating-said `gimball aboutsaid' third axisin accordance 30 with the roll angle of saidi `craft whereby-to maintain said rotor spinaxishorizontal:

21111 an azimuth reference` system for navigable craft the-combination comprising# a flux valve for supplying a signalfupon changes inthe azimuth-all orientation of said cra-fti relative to magnetic north; means ,responsivey to saidr fluir valve signal `for supplying a first `controllsignalL corre-, sponding toV the difference betweentthe existing,` azimuthal` orientation and a desired azimuthal orientation *of said" craft rel-'attivatol magnetic north,` a directional gyroscope, el() means controlled by the orientation of" said-gyra andi:` responsive to sai-d first control signal for `derivi-ng a second control signal corresponding `to the diiferencebetween the orientation of said gyro and the desired orientation .of IH said craft as determined by said"firstdiierencefsignal; i0 andmeans--responsive to said second signal for precessingsaid gyroscope in. azimuth in a directionu and to anfarnount` to reduce said- ,seconddilference signal, bot-h. of"saiduI signals` being zero when the orientationfoftsaidt gyrol l l corresponds to the-desired azimuthal orientation-'of' said-f 'Of craft,

3. `An azimuth `reference `system` forv navigable craft comprising a flux `valve for supplying asignal` with i changes inthe azimuthal orientation of said craft relattveto `magnetic northmeans responsive to said `ilux` valve! 51 signal for supplying a iirst` control signal corresponding'f` 1 to the difference between, zin-existing andi a desired: azimuthal; orientation of said craft relative-` tomagnetic north, `a directional `gyroscope, means controlled by the` orientation ofssaid gyrojand responsive to;` said control ,60V

signal forderiving a second `control signal-corresponding t to thediiference between the orientation-of saidf gyro4 and the desired orientation of saidfcraft, means responsive to said second signal for'precessingisaid gyroscope in,`

azimuth in a direction and to an amount to reduce` said 615,1`

second signal toward `zero whereby to orientate said gyroscope in accordance with-the desired azimut-hal orion-` tation of` said craft, andmeans-responsive to the azimuthal! t orientation of said-gyroscope fortsnpplyinga craft control signal whereby to control said craft orientation in accordancewith the orientation of` said` gYrOsCope to thereby reduce said rstcontrol signal to zero.

4. An azimuth reference systemfor an automatic -pilot for-aircraftharing` control surfaQes--anclfactuatn "means t craft, said system comprising a fluir' valve for"-`su`'p`p1ying`-l a signalwith changes inthe azimuthalorientationof"` said craftrelative to magnetic north, ay directional gyroscope and means for processing the same in azimuth, means for supplying an azimuth command signal proportional to a desired azimuthal orientationof' said craft,

means responsive to` said ux valve signal and controlledV by said command signal for supplying a rst control signal proportional' to the difference therebetween, means for supplying said first control` signal to said' gyro processing means for processing said` gyro in azimuth"H whereby said gyro orientation is `coutrolledin accordance with the desired orientation of'said craft, means respon-` sive to said gyro orientation for supplying a second tionv of:4 said gyro to thereby reduce said first control` signal toward zero.

5. In an automatic pilot for aircraft having controlf surfaces for controlling the azimuthal orientation o f saidl craft and-actuating means therefor, the comhinationcomrprising a ilux valve for supplying a signal with changesl in the azimuthal orientation of" said craft relative toI magnetic north, means for supplyingy anazimuth com-v mand signal` proportional to a desired craft orientations" motive means responsive to said command signal and' including means responsive to the operation thereof for reducing sadcomrnand signaltoward zero, meansrespon sive to said flux-valve signal and controlled by said motor means for supplying a first controlfsignaltproportionalto i the difference between present craft orientation andtheV desired orientation thereof, a` directional gyro, means responsive to said lirst control signal andcontrolled by said control surface actuating means whereby tocontrol-` the orientation of said1 craft in. accordance with the-t orientation of said-gyro to `thereby reduce said first control?? signa-ll toward zero.

6. Automatic pilot means of the character set forthin` claim; 5` comprisingfurther means responsive to 'turning of said craft for regulating the operation of said* motor means.-

7-. A heading reference foraircraft comprisingfa-magA netic reference device for supplying a signal which changes with the orientation of said craft in-yawrelative5 to magnetic` north, meansresponsive to said signal for supplying a firstoontrol signalfcorresponding-to a desiredtheadingy of said craft'relative tomagnetic north, a directional gyroscopehaving a` rotor, a rotor bearing case` supporting said t roto-r; for `spinningnabout a first,` axisl` normally-parallelftothe-pitch axis-of` said craft, a gimbal( for pivotally supportingsaidirotor` casefor angular-move#- ment about a second axis normally parallel.` to said yawf axis ofwsaid craft," means for pivotally supporting tho-- gimbalfor angular movement about a thirdtaxis parallel tothe-craft `roll axis, means responsive tosaidfirst con-` trol signal `for, processing said spin axisrabout saidsecondE axis` in a direction` and to` an amount to reduce said;` rst-control--signal to-zero whereby to orientate. the-- spin axis of said gyro` in` accordance with the desiredheading: of said,` craft, a: horizontal reference device'wforr" supplyinga second control signal upon` changes; infthe` position off said craft: about said `roll raxis relative` `to other horizon,` and-means responsive tosaidsecond control' signal-for processing-said spin axis about said'third axisw upon changes in the roll attitude of said; craft whereby*-N tormaintain said` spin axis` horizontal.

8. 'An-automatic pilotfor` aircraftl1aving control surf.

11 faces for controlling the bank'and yaw attitude of said aircraft, a magnetic reference device for providing a first signal proportional to the azimuthal orientation of said craft relative to magnetic north, a directional gyro having a rotor, a rotor-bearing case supporting said rotor for spinning about a horizontal axis, a gimbal pivotally supporting said rotor case for angular movement about a second normally vertical axis, means for supporting said gimbal in said aircraft for pivotal movement about a third axis parallel to the longitudinal axis of said aircraft,

Vmeans for supplying a second signal proportional to a dcsired orientation of said aircraft, means responsive to said rst signal and controlled by said second signal for providing a third signal proportional to the difference between an existing orientation of said craft and the desired orientation thereof, means for precessing said gyro about said secondv axis in accordance with said third signal, means responsive to the orientation of said gyro about said second axis for controlling said lyaw control surface, further means responsive to Said first signal for controlling said bank control surface whereby to cause said craft to bank and turn to ythereby reduce said third signal, and means responsive to banking of said craft for precessing said gyro about said third axis in accordance with the craft bank angle whereby to maintain said gyro spin axis horizontal during turning of said craft.

9. An automatic pilot of the character set forth in claim 8 wherein said last-mentioned means comprises a vertical gyro having means for supplying a signal proportionalY to the bank angle of said craft and means coupled with said directional gyro and responsive to said bank angle signal for precessing the same about said third axis thereof in accordance with the blank angle of said craft.

l0. Gyroscopic reference apparatus for aircraft comprisiug, a rotor, an inner gimbal supporting said rotor for spinning about a normally horizontal axis, an outer gimbal pivotally supporting said inner gimbal for angular movement about a second normally vertical axis, means pivotally supporting said outer gimbal in said craft for angular movement about a third, axis parallel to the craft longitudinal axis whereby said spin axis is normally perpendicular to said second and third axes, means responsive to turning of said craft, precessing means controlled by said turn-responsive means for maintaining said spin axis perpendicular to said second and third axes, and precessing means for positioning said outer` gimbal, a gyro vertical for providing a signal proportlonal to craft bank angle, and means for controlling said outer gimbal precessing means in accordance with said -bank signal whereby to maintain the pivotal axis for said vided by said heading reference means upon actuationv thereof, a bank command follow-up motive means having an output thereof connected to alter the reference provided by said bank reference means upon actuation thereof, turn command means, means coupled between said turn command means and the output of said heading follow-up motive means for providing lirst and second signals each corresponding to the error therebetween, means supplying said first signal to said heading follow-f up motive means in a sense to reduce the same towards zero and at a rate determined by the magnitude thereof, means coupled with the output of said bank follow-up motive means and responsive to said second signal for supplying a third signal corresponding to the error therebetween, and means for supplying said third signal to said bank follow-up motive means in a sense to reduce tlie same towards zero.

12. In an automatic pilot'of the character set forth in claim 11 wherein said turn command means comprises a heading selector, wherein said first-mentioned error corresponds to an angle proportional to the difference between the existing craft heading and a selected heading thereofand wherein the means for supplying said tirst v signal to said heading follow-up motive means includes a limiter for limiting the magnitude of said first signal to a predetermined maximum value whereby to limit the rate of operation of said heading follow-up motive means to a predetermined value for all values of said first signal greater than said limited value.

ing an additional signal proportional to lateral accelera- `tions of said aircraft and means for further controlling said heading follow-up motive means in accordance therewith.

14. The combination in a gyroscopic reference apparatus for aircraft comprising, a gyro vertical having mutually perpendicular normally horizontal axes corresponding to the pitch and roll axes of the aircraft and pick-off devices providing signals respectively proportional to deviations of the aircraft from a level flight attitude condition about said pitch and roll axes, a `three degree of freedom gyroscope having a rotor, a rotor case and a gimbal ring therefor, said gimbal ring being pivotally supported in said craft for freedom about an axis substantially parallel to one of the normally horizontal axes of said vertical gyro, and means responsive to the signal of scope having a gimbal ring pivotally supported in saidl craft for freedom about an axis substantially parallel to one of the normally horizontal axes of said vertical gyro, a rotor case pivotally supported in said gimbal ring with freedom about an axis normally parallel to the reference axis established by said vertical gyro, means responsive to the signal of one of said gyro vertical pickof devices for stabilizing said gimbal ring about an axis p substantially parallel to one of said gyro vertical support axes, and means responsiveto turning of said craft for maintaining said rotor case in a predetermined angular relation with respect to said gimbal ring.

16. A gyroscopic reference system for aircraft comprising, a vertical gyroscope for defining a vertical'reference axis, signal generating means coupled with said gyroscope for providing a signal proportional to the bank angle of said craft, a three degree of freedom gyroscope having a gimbal ring pivotally supported in said craft with freedom about an axis substantially parallel to the roll axis of said craft, a rotor and rotor bearing case, said case being pivotally supported in said gimbal ring for freedom about an axis normally perpendicular to said gimbal support axis and said rotor being supported in said case such that its spin axis is normally mutually perpendicular to both said gimbal and rotor case support axes, means responsive to said signal generator for tilting said gimbal in accordance with the bank angle of said craft, and means responsive to turning ofsaid craft for' maintaining said spin axis substantially mutually perpendicular to said gimbal and rotor case support axes.

References Cited in the tile of this patent UNITED STATES PATENTS p 2,005,530 Boykow Iune 18. 1935 2,493,015 Newton- Jan. 3,1950 

